As observed, reported and learned from nine California earthquakes since 1951, existing Portland cement-based exterior plaster (stucco) of wooden-framed structures has had little success in surviving intense lateral loads caused by earthquake, as well as hurricane forces. For example, the shaking intensity during the 1994 Northridge Earthquake, which in some locations reached magnitudes of 8 and 9 Modified Mercalli Intensity (MMI), was enough to detach stucco sheathings from the wooden frame of many one and two story single family residences and apartment buildings. Such detachment of the stucco sheathings from the wood framing resulted in heavy interior damage, uninhabitable structures and required the removal and replacement of the stucco sheathings.
A primary reason for the detachment of the stucco from the wood framing was the Uniform Building Code's approval of staples, since 1957, for attaching a reinforcing wire mesh to the wood framing prior to applying the stucco over the wire mesh coupled with the requirement of the Uniform Building Code in 1967 that a 26 gauge corrosion resisting continuous drip screed be installed against the mud sill plate, which is disposed along the lower portion of the wood framing. The mud sill plate has a minimum of a one inch overlap below the wood sill plate. The continuous drip screed is typically attached to the mud sill by the use of nails so that the stucco ends evenly just below the mud sill. Waterproof building paper and wire mesh or metal lath are then installed over the drip screed.
The wire mesh or metal lath is normally attached to the metal drip screed by use of the Uniform Building Code's specified staples, which are typically applied by use of a staple gun. Many times, the staple legs become bent and do not penetrate the metal drip screed. Staples used to fasten the wire mesh at the drip screed are often rusted out within a few years due to moisture rusting and weakening the thin staple legs. Stucco having poor lateral attachment to the mud sill due to unattached or rusted staples, typically fails at the wood sill plate during intense lateral displacement of the wood framing generated by such forces as earthquakes and/or hurricanes. Failure of the stucco sheathing generally results in heavy structural damage, often leaving the structure uninhabitable and needing complete replacement of the exterior stucco sheathing.
More recently, particularly in structures built after 1994, home builders have had limited success in improving the structural strength of the stucco sheathings by using furring nails to reinforce the wire mesh to the wood framing. Such nails are the subject of U.S. Pat. No. 1,517,035, wherein the head of the nail and a spacer concentrically disposed around the nail are configured to both retain the wire mesh and maintain the wire mesh at a distance apart from the underlying structure, or building paper, when the nail is driven into place within the framing. However, the use of such furring nails is labor intensive and cannot be retrofitted to strengthen existing stucco wall sheathings.
Therefore there is a need for a device and method of improving the strength of existing stucco sheathing against intense lateral forces, which is inexpensive and easily retrofitted to existing stucco sheathings.